Use Alias in common.opt to make -ftree-loop-linear an alias of -floop-interchange.

Use Alias in common.opt to make -ftree-loop-linear an alias of -floop-interchange.

2011-01-31  Sebastian Pop  <sebastian.pop@amd.com>

	* common.opt (ftree-loop-linear): Use Alias to make it an alias of
	-floop-interchange.
	* invoke.texi (-ftree-loop-linear): Make it clear that this flag
	is an alias of -floop-interchange and that it requires the
	Graphite infrastructure.
	* tree-ssa-loop.c (gate_graphite_transforms): Do not set
	flag_loop_interchange based on the value of flag_tree_loop_linear.

From-SVN: r169445